Tone deafness shows up in the brain

If you always thought there was something the matter with your tone-deaf friends, research has now backed you up: they seem to be lacking some brain material.

Scientists in Montreal, Canada, and Newcastle in the United Kingdom have identified the part of the brain that causes some people to sing like larks and others to make you run for your earplugs as soon as they pick up the karaoke microphone. Krista Hyde at the Montreal Neurological Institute and her colleagues used magnetic resonance imaging (MRI) to study the brains of tone deaf, or amusic, people and compared the images with others from people with normal musical ability.

The studies from both countries used identical methods and each set of results highlighted an area in the front of the brain the right inferior frontal gyrus which contains less white matter in amusic people than in the musically normal.

White matter is responsible for information transmission in the brain, and the deficiency seen by Hyde probably hampers communication in the brain's right hemisphere, the researchers suggest, making music comprehension difficult.

I've got rhythm

Musical 'behaviour' is often quantified by standard tests for six different abilities, including a sense of metre, the ability to remember a tune, and the ability to decipher changes in key, pitch, pitch direction and rhythm.

The amount of white matter in the brain matches up with the tests for melody, rather than rhythm, the research in Brain1 reveals. This is consistent with previous work showing that tone deafness is largely a pitch-based condition.

The new work shows a crucial link between musical behaviour and anatomy, which could prove a real breakthrough in understanding the condition, says Hyde.

The work is interesting, says Andrew Blamire, who does brain research at Newcastle University's Magnetic Resonance Centre, because it looks for changes in anatomy rather than changes in how the brain responds when actively listening to music. A scan of amusical brains taken when the volunteers were trying to sing, for example, would not have shown up this difference in white matter.

He's surprised that the change doesn't show up in the auditory cortex.

Genetic condition

To improve the results, Blamire suggests using a technique called 'diffusion tensor imaging', which gives more details about what's happening in the white matter, allowing scientists to track how one part of the brain links up with another.

Hyde has begun doing just this, and is working to verify her hunch that amusia is genetic, in a similar way to dyslexia.

She has recently discovered that the cortical thickness in the same region of the brain is also linked to the behavioural tests. "This is something that the genes might control," she says. "It really is an open story, but we favour this idea that it might be congenital" that is, present from birth. The other suggestion is that musicality can be trained, and with exposure to more music, more of the relevant white matter grows.

Hyde is determined to solve the problem, to try and improve the quality of life of the amusic group she's been working with for five years. "It's such a difficulty not to enjoy and perceive music," she says.